Thermoacoustic apparatus and thermoacoustic system

ABSTRACT

In a thermoacoustic apparatus including a loop tube, a standing wave and a traveling wave are generated rapidly and, thereby, heat exchange is performed rapidly and efficiently. The thermoacoustic apparatus includes a first stack  3   a  sandwiched between a first high-temperature-side heat exchanger  4  and a first low-temperature-side heat exchanger  5  and a second stack  3   b  sandwiched between a second high-temperature-side heat exchanger  6  and a second low-temperature-side heat exchanger  7  in the inside of a loop tube  2 . An acoustic wave is generated through self excitation by heating the first high-temperature-side heat exchanger  4 , and the second low-temperature-side heat exchanger  7  is cooled by a standing wave and a traveling wave. The loop tube is configured to include a plurality of linear tube portions  2   a  along the vertical direction and connection tube portions  2   b  shorter than the linear tube portions  2   a , and the first stack  3   a  is disposed in the longest linear tube portion  2   a.

TECHNICAL FIELD

The present invention relates to a thermoacoustic apparatus capable ofcooling or heating an object through the use of thermoacoustic effectand a thermoacoustic system including the thermoacoustic apparatus.

BACKGROUND ART

Known technologies of a heat exchanger through the use of thermoacousticeffect include the technologies described in the following PatentDocument 1, Non-Patent Document 1, and the like.

The apparatus described in Patent Document 1 relates to a coolingapparatus through the use of thermoacoustic effect. This apparatus isconfigured to include a first stack sandwiched between ahigh-temperature-side heat exchanger and a low-temperature-side heatexchanger and a regenerator sandwiched between a high-temperature-sideheat exchanger and a low-temperature-side heat exchanger in the insideof a loop tube, in which a working fluid is enclosed, where an acousticwave is generated through self excitation by heating thehigh-temperature-side heat exchanger on the first stack side, and thelow-temperature-side heat exchanger on the regenerator side is cooled bya standing wave and a traveling wave based on the acoustic wave.

Likewise, Non-Patent Document 1 discloses an experimental study of acooling apparatus through the use of thermoacoustic effect. The coolingapparatus used in this experiment is also configured to include asubstantially rectangular cross-section loop tube formed from a metal, afirst stack sandwiched between a heater (high-temperature-side heatexchanger) and a low-temperature-side heat exchanger, and a second stackdisposed at a position opposite to the first stack. A temperaturegradient is generated in the first stack by heating the heater(high-temperature-side heat exchanger) disposed on the first stack sideand, in addition, circulating running water in the low-temperature-sideheat exchanger, and an acoustic wave is generated through selfexcitation in a direction opposite to the temperature gradient. Theresulting acoustic energy is transferred to the regenerator side throughthe loop tube, and on the second stack side, thermal energy istransferred in the direction opposite to the direction of the acousticenergy on the basis of the energy conservation law, so as to cool thevicinity of a thermometer on the other end side of the second stack.According to this document, a temperature reduction of about 16° C. hasbeen ascertained under a predetermined condition at the portion wherethe thermometer has been disposed.

Patent Document 1: Japanese Unexamined Patent Application PublicationNo. 2000-88378

Non-Patent Document 1: Shinichi SAKAMOTO, Kazuhiro MURAKAMI, andYoshiaki WATANABE, “Netsuonkyou Koukao Mochiita Onkyoureikyaku GenshounoJikkenteki Kentou (Experimental Study of Acoustic Cooling PhenomenonThrough the Use of Thermoacoustic Effect)”, The Institute ofElectronics, Information and Communication Engineers, TECHNICAL REPORTOF IEICE. US2002-118 (2003-02)

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

In the apparatus through the use of the above-described thermoacousticeffect, the time period from heating to generation of the standing waveand the traveling wave must be reduced. Furthermore, after the standingwave and the traveling wave are generated, the efficiency of heatexchange must be improved. In the case where the standing wave and thetraveling wave are generated rapidly, it is necessary that, for example,the temperature gradient is formed in the stack as rapid as possible andthe surface wavefront of the generated acoustic wave is stabilized asrapid as possible.

However, in the above-described Patent Document 1, since the first stackserving as a generation source of an acoustic wave is disposed in ahorizontal linear tube portion relative to the ground, the heat inputinto the high-temperature-side heat exchanger of the first stack spreadsin a horizontal direction in the linear tube portion and, therefore, theheat enters the first stack, so that a large temperature gradient cannotbe generated in the stack. Consequently, it takes much time until anacoustic wave is generated through self excitation, and there is aproblem in that the cooling efficiency cannot be improved. In order togenerate the standing wave and the traveling wave rapidly, it isnecessary to stabilize the surface wavefront of the acoustic wavegenerated in the first stack as rapid as possible. However, if thedistance from the first stack to the corner portion of the loop tube issmall, the surface wavefront before being stabilized is reflected at thecorner portion of the loop tube, the surface wavefront is disturbed, andthere is a problem in that it takes much time until an acoustic wave isgenerated through self excitation.

Accordingly, in order to overcome the above-described problems, it is anobject of the present invention to provide a thermoacoustic apparatusincluding a loop tube, wherein a standing wave and a traveling wave aregenerated rapidly and, thereby, heat exchange is performed rapidly andefficiently.

MEANS FOR SOLVING THE PROBLEMS

In order to overcome the above-described problems, a thermoacousticapparatus according to an aspect of the present invention includes afirst stack sandwiched between a first high-temperature-side heatexchanger and a first low-temperature-side heat exchanger and a secondstack sandwiched between a second high-temperature-side heat exchangerand a second low-temperature-side heat exchanger in the inside of a looptube, wherein a standing wave and a traveling wave are generated throughself excitation by heating the above-described firsthigh-temperature-side heat exchanger, the above-described secondlow-temperature-side heat exchanger is cooled by the standing wave andthe traveling wave, or/and a standing wave and a traveling wave aregenerated through self excitation by cooling the above-described firstlow-temperature-side heat exchanger, and the above-described secondhigh-temperature-side heat exchanger is heated by the standing wave andthe traveling wave, and in the thermoacoustic apparatus, theabove-described loop tube is configured to include a plurality of lineartube portions, which stand relative to the ground, and connection tubeportions shorter than the linear tube portions, and the above-describedfirst stack is disposed in the longest linear tube portion among theplurality of linear tube portions.

According to this configuration, the surface wavefront of the acousticwave generated in the first stack can be stabilized in the linear tubeportion set to be the longest, and the standing wave and the travelingwave can be generated rapidly. Since the first stack is disposed in thelinear tube portion standing relative to the ground, the time until theacoustic wave is generated can be reduced through the use of an updraftor a downdraft generated on the first stack side. Furthermore, after thestanding wave and the traveling wave are generated, the efficiency ofheat exchange can be improved.

When the lengths of the linear tube portion and the connection tubeportion of the above-described loop tube are assumed to be La and Lb,respectively, the lengths are set in such a way as to satisfy1:0.01≦La:Lb<1:1.

According to this configuration, since the linear tube portion becomesrelatively long, as in the above description, the surface wavefront ofthe acoustic wave can be stabilized. It is preferable that the lineartube portion is as long as possible, and when the lengths are set insuch a way as to satisfy La:Lb≦1:0.5, the surface wavefront of thegenerated acoustic wave can be further stabilized.

In the above-described apparatus, in the case where the firsthigh-temperature-side heat exchanger is heated and the secondlow-temperature-side heat exchanger is cooled, the first stack isdisposed below the center of the linear tube portion.

According to this configuration, a large space for generation of anupdraft due to the heat applied to the first high-temperature-side heatexchanger can be ensured in the upside, and the standing wave and thetraveling wave can be generated rapidly through the use of the updraft.

Moreover, in the case where the first low-temperature-side heatexchanger is cooled and the second high-temperature-side heat exchangeris heated, the first stack is disposed above the center of the lineartube portion.

According to this configuration, a large space for generation of adowndraft due to the heat at a low temperature (hereafter referred to as“low-temperature heat”) applied to the first low-temperature-side heatexchanger can be ensured in the downside, and the standing wave and thetraveling wave can be generated rapidly through the use of thedowndraft.

When one end of the linear tube portion is connected to one end of theconnection tube portion, an intersection of the respective center axesis assumed to be a start point of a circuit, and an entire length of thecircuit is assumed to be 1.00, the center of the first stack is set at aposition corresponding to 0.28±0.05 relative to the entire length of thecircuit.

According to this configuration, when the respective temperatures of thefirst high-temperature-side heat exchanger and the firstlow-temperature-side heat exchanger in the first stack are appropriate,the acoustic wave can be generated through self excitation more rapidly.

When an entire length of the circuit is assumed to be 1.00, a first peakof the pressure variation of a working fluid along the circuit ispresent in the vicinity of the first stack, and a second peak is presentat a position corresponding to about one-half the entire length of thecircuit, the above-described second stack is disposed in such a way thatthe center of the second stack is positioned past the above-describedsecond peak.

According to this configuration, the cooling efficiency or the heatingefficiency in the second stack can be increased.

An acoustic wave generator for generating the standing wave and thetraveling wave is disposed on the outer perimeter portion or in theinside of the loop tube.

According to this configuration, the standing wave and the travelingwave can be generated more rapidly not only by the acoustic wave throughself excitation, but also by forced vibration from the acoustic wavegenerator.

The first stack or/and the second stack to be used include connectionchannels arranged in such a way that the inner diameters of individualconnection channels are increased one after another as the position ofthe connection channel approaches the outside.

When such a stack is used, since the inner diameters of the connectionchannels in the vicinity of the boundary layer in the inside of the looptube can be increased, the energy exchange in this portion can beperformed efficiently.

Alternatively, the first stack or/and the second stack to be usedinclude connection channels arranged in such a way that the innerdiameters of individual connection channels are decreased one afteranother as the position of the connection channel approaches theoutside.

When such a stack is used, since the inner diameters of the connectionchannels in the center portion in the inside of the loop tube can beincreased, the energy exchange in this center portion can be performedefficiently.

Alternatively, the first stack or/and the second stack to be usedinclude meandering connection channels.

When such a stack is used, since large surface areas of the workingfluid and the stack can be ensured, the heat exchange with the workingfluid is facilitated and, thereby, higher-temperature heat can beoutput.

Alternatively, the first stack or/and the second stack to be usedinclude connection channels arranged in such a way that the flow pathlengths of individual connection channels are decreased one afteranother as the position of the connection channel approaches theoutside.

When such a stack is used, the flow path lengths of connection channelsclose to the boundary layer of the loop tube are decreased, the speedgradient can be made uniform and, thereby, the heat exchanger can beheated or cooled uniformly.

The thermoacoustic apparatus according to an aspect of the invention, inwhich a material for the first stack or/and the second stack is composedof at least one type of ceramic, sintered metal, gauze, and nonwovenmetal fabric, and the ωτ (ω: an angular frequency of the working fluid,τ: temperature relaxation time) thereof is configured to become withinthe range of 0.2 to 20.

According to this configuration, an acoustic wave can be generatedthrough self excitation more rapidly and efficiently.

Furthermore, a plurality of the above-described thermoacousticapparatuses are disposed, wherein a second low-temperature-side heatexchanger in one thermoacoustic apparatus is connected to a firstlow-temperature-side heat exchanger in another thermoacoustic apparatusadjacent thereto, or a second high-temperature-side heat exchanger inone thermoacoustic apparatus is connected to a firsthigh-temperature-side heat exchanger in another thermoacoustic apparatusadjacent thereto.

According to this configuration, since the temperature gradient in thefirst stack is increased one after another on an adjacent thermoacousticapparatus basis, higher-temperature heat or lower-temperature heat canbe output from the thermoacoustic apparatus on the end side.

Advantages

The thermoacoustic apparatus according to an aspect of the presentinvention includes the first stack sandwiched between the firsthigh-temperature-side heat exchanger and the first low-temperature-sideheat exchanger and the second stack sandwiched between the secondhigh-temperature-side heat exchanger and the second low-temperature-sideheat exchanger in the inside of the loop tube, wherein a standing waveand a traveling wave are generated through self excitation by heatingthe above-described first high-temperature-side heat exchanger, theabove-described second low-temperature-side heat exchanger is cooled bythe standing wave and the traveling wave, or/and a standing wave and atraveling wave are generated through self excitation by cooling theabove-described first low-temperature-side heat exchanger, and theabove-described second high-temperature-side heat exchanger is heated bythe standing wave and the traveling wave, and in the thermoacousticapparatus, the above-described loop tube is configured to include aplurality of linear tube portions, which stand relative to the ground,and connection tube portions shorter than the linear tube portions, andthe above-described first stack is disposed in the longest linear tubeportion among the plurality of linear tube portions. Consequently, thesurface wavefront of the acoustic wave generated in the first stackthrough self excitation can be stabilized in the long linear tubeportion, and the standing wave and the traveling wave can be generatedrapidly. Since the first stack is disposed in the standing linear tubeportion, the time until the acoustic wave is generated can be reducedthrough the use of an updraft or a downdraft generated on the firststack side. Furthermore, after the acoustic wave is generated, theefficiency of heat exchange can be improved.

BEST MODE FOR CARRYING OUT THE INVENTION

A first embodiment of a thermoacoustic apparatus 1 according to anaspect of the present invention will be described below with referenceto drawings.

As shown in FIG. 1, the thermoacoustic apparatus 1 in the presentembodiment includes a first stack 3 a sandwiched between a firsthigh-temperature-side heat exchanger 4 and a first low-temperature-sideheat exchanger 5 and a second stack 3 b sandwiched between a secondhigh-temperature-side heat exchanger 6 and a second low-temperature-sideheat exchanger 7 in the inside of a loop tube 2 configured to take on arectangular shape as a whole. A standing wave and a traveling wave aregenerated through self excitation by heating the firsthigh-temperature-side heat exchanger 4 on the first stack 3 a side, andthe second low-temperature-side heat exchanger 7 disposed on the secondstack 3 b side is cooled by propagating the standing wave and thetraveling wave to the second stack 3 b side.

In the present embodiment, in order to reduce the time from the heatingof the first high-temperature-side heat exchanger 4 until the standingwave and the traveling wave are generated, a pair of linear tubeportions 2 a are disposed along the vertical direction (direction ofgravity), connection tube portions 2 b shorter than these linear tubeportions 2 a are disposed, and the first stack 3 a is disposed in thelower portion of one of the linear tube portions 2 a while beingsandwiched between the first high-temperature-side heat exchanger 4 andthe first low-temperature-side heat exchanger 5.

The surface wavefront of the acoustic wave generated from the firststack 3 a must be stabilized as rapid as possible in order to generate astanding wave and a traveling wave. However, if the length of the lineartube portion 2 a, in which the first stack 3 a is disposed, is small,the acoustic wave is reflected at corner portions 20 b disposed bothends of the connection tube portion 2 b, and the surface wavefront isdisturbed due to phase inversion or the like. Therefore, in the presentembodiment, the first stack 3 a is disposed in the longest linear tubeportion 2 a in the loop tube 2 in order to stabilize the surfacewavefront of the generated acoustic wave as rapid as possible. Thelength of this linear tube portion 2 a is set to be longer than thelength of the connection tube portion 2 b, and when the length of thelinear tube portion 2 a is assumed to be La and the length of theconnection tube portion 2 b is assumed to be Lb,

La and Lb are set within the range satisfying1:0.01≦La:Lb<1:1.

However, it is preferable that the linear tube portion 2 a is made aslong as possible, and

La and Lb are set within the range satisfying1:0.01≦La:Lb≦1:0.5.

On the other hand, the connection tube portion 2 b connecting the lineartube portions 2 a is configured to have corner portions 20 b at bothends. The acoustic wave propagated from the linear tube portion 2 a isreflected by the corner portion 20 b to the connection tube portion 2 b.With respect to the configuration of the corner portion 20 b, in orderto reflect the acoustic wave efficiently to the connection tube portion2 b, a structure shown in FIG. 2 is used. FIG. 2 is a diagram showing amagnified corner portion 20 b in the upper end portion of the lineartube portion 2 a. Since configurations similar to the configuration ofthis corner portion 20 b are used for the other corner portions 20 b,explanations of the configuration of the corner portions 20 b in otherportions will not be provided. In FIG. 2, the corner portion 20 b isconfigured to have an inner diameter substantially equal to the innerdiameter of the linear tube portion 2 a and have a diameter which issubstantially equal to the inner diameter of the tube and which iscentering the inside corner portion of the loop tube 2. In this manner,all the acoustic energy transferred from the linear tube portion 2 a isreflected at the corner portion 20 b, and is transferred to theconnection tube portion 2 b side without being returned to the lineartube portion 2 a. Furthermore, the inner diameter of the corner portion20 b is configured to become substantially equal to that of the lineartube portion 2 a and, thereby, the inner walls of the linear tubeportion 2 a and the corner portion 20 b can be made smooth.Consequently, the acoustic energy is prevented from being lost, so thatthe acoustic energy can be transferred efficiently. The shape of thiscorner portion 20 b is not limited to an arch shape, and a linear shapeas shown in FIG. 3 can also be used. FIG. 3 is a diagram showing amagnified corner portion 200 b in the upper end portion of the lineartube portion 2 a. In FIG. 3, the corner portion 200 b is disposed insuch a way that the outside corner portion thereof takes on a shape of astraight line which forms an angle of about 45 degrees with the lineartube portion 2 a. Consequently, all the acoustic wave propagating in thelinear tube portion 2 a is reflected at this linear corner portion tothe connection tube portion 2 b side.

These linear tube portion 2 a and connection tube portion 2 b arecomposed of metal pipes. However, the material is not limited to themetal or the like, and may be transparent glass, a resin, or the like.When these portions are composed of a material, such as the transparentglass, the resin, or the like, positions of the first stack 3 a and thesecond stack 3 b can be checked and the status in the tube can easily beobserved in an experiment or the like.

In the inside of the thus configured loop tube 2, the first stack 3 asandwiched between the first high-temperature-side heat exchanger 4 andthe first low-temperature-side heat exchanger 5 and the second stack 3 bsandwiched between the second high-temperature-side heat exchanger 6 andthe second low-temperature-side heat exchanger 7 are disposed.

This first stack 3 a is configured to take on a cylindrical shape whichtouches the inner wall of the loop tube 2, and is formed from amaterial, e.g., ceramic, sintered metal, gauze, or nonwoven metalfabric, which has a large heat capacity. The first stack 3 a isconfigured to have multiple holes penetrating in the axis direction ofthe loop tube. As shown in FIG. 4 and FIG. 5, a stack 3 c including aplurality of connection channels 30 arranged in such a way that theinner diameters of individual connection channels are increased oneafter another as the position of the connection channel approaches theoutside from the center or a stack 3 d including connection channels 30arranged in such a way that the inner diameters of individual connectionchannels are decreased one after another as the position of theconnection channel approaches the outside from the center can be used inplace of this first stack 3 a. Alternatively, as shown in FIG. 6 andFIG. 7, a stack 3 e including meandering connection channels 30(connection channel 30 indicated by a thick line) produced by laying,for example, a plurality of fine spherical ceramic or a stack 3 fincluding connection channels 30 arranged in such a way that the flowpath lengths of individual connection channels are decreased one afteranother as the position of the connection channel approaches the innerperimeter surface of the loop tube 2 may be used.

Both the first high-temperature-side heat exchanger 4 and the firstlow-temperature-side heat exchanger 5 are composed of a thin metal, andare configured to include through holes for transmitting the standingwave and the traveling wave in the inside thereof. Among these heatexchangers, the first high-temperature-side heat exchanger 4 isconfigured to be heated by an electric power supplied from the outside,waste heat, unused energy, or the like. On the other hand, the firstlow-temperature-side heat exchanger 5 is set at a temperature relativelylower than that of the first high-temperature-side heat exchanger 4 bycirculating water around it.

The first stack 3 a sandwiched between the first high-temperature-sideheat exchanger 4 and the first low-temperature-side heat exchanger 5, asdescribed above, is disposed below the center of the linear tube portion2 a while the first high-temperature-side heat exchanger 4 is disposedon the upper side. The first stack 3 a is disposed below the center ofthe linear tube portion 2 a, as described above, on the grounds that anacoustic wave is generated rapidly through the use of an updraftgenerated when the first high-temperature-side heat exchanger 4 isheated. The first high-temperature-side heat exchanger 4 is disposed onthe upper side on the grounds that a warm working fluid generated whenthe first high-temperature-side heat exchanger 4 is heated is preventedfrom entering the first stack 3 a and, thereby, a large temperaturegradient is formed between the first low-temperature-side heat exchanger5 and the first high-temperature-side heat exchanger 4.

With respect to the condition for the generation of the acoustic wavethrough self excitation in the first stack 3 a, in the case where theworking fluid flows in the first stack 3 a, when a flow path radius ofthe parallel channels is assumed to be r, an angular frequency of theworking fluid is assumed to be ω, a temperature diffusion coefficient isassumed to be α, and a temperature relaxation time is assumed to be τ(=r²/2α), the acoustic wave can be generated through self excitationmost efficiently when ωτ is within the range of 0.2 to 20. Therefore, r,ω, and τ are set in such a way as to satisfy these relationships.Furthermore, when one end of the linear tube portion 2 a is connected toone end of the connection tube portion 2 b in FIG. 2, an intersection ofthe respective center axes is assumed to be a start point X of acircuit, and an entire length of the circuit is assumed to be 1.00, theacoustic wave can be generated through self excitation more rapidly andefficiently by setting the center of the first stack at a positioncorresponding to 0.28±0.05 relative to the entire length of the circuitin a counterclockwise direction from the start point X.

On the other hand, similarly to the first stack 3 a, the second stack 3b is configured to take on a cylindrical shape which touches the innerwall of the loop tube 2, and is formed from a material, e.g., ceramic,sintered metal, gauze, or nonwoven metal fabric, which has a large heatcapacity. The second stack 3 b is configured to have multiple holespenetrating in the axis direction of the loop tube. This second stack 3b is disposed in such a way that when a first peak of the pressurevariation of the working fluid along the loop tube 2 is present in thevicinity of the first stack 3 a, and a second peak is present at aposition corresponding to about one-half the entire length of thecircuit, the center of the second stack 3 b is positioned past thesecond peak. As shown in FIG. 4 and FIG. 5, a stack 3 c including aplurality of connection channels 30 arranged in such a way that theinner diameters of individual connection channels are increased oneafter another as the position of the connection channel approaches theoutside from the center or a stack 3 d including connection channels 30arranged in such a way that the inner diameters of individual connectionchannels are decreased one after another as the position of theconnection channel approaches the outside from the center can be used inplace of this second stack 3 b similarly to that for the first stack 3a. Alternatively, as shown in FIG. 6 and FIG. 7, a stack 3 e includingmeandering connection channels 30 (connection channel 30 indicated by athick line) produced by laying, for example, a plurality of finespherical ceramic or a stack 3 f including connection channels 30arranged in such a way that the flow path lengths of individualconnection channels are decreased one after another as the position ofthe connection channel approaches the inner perimeter surface of theloop tube 2 may be used.

Likewise, both the second high-temperature-side heat exchanger 6 and thesecond low-temperature-side heat exchanger 7 disposed on the secondstack 3 b side are composed of a thin metal, and are configured toinclude through holes for transmitting the standing wave and thetraveling wave in the inside thereof. Water is circulated around thesecond high-temperature-side heat exchanger 6 and, in addition, anobject of cooling is connected to the second low-temperature-side heatexchanger 7. It is believed that the object of cooling is outside air, aheat-producing household electric appliance, a CPU of a personalcomputer, and the like. However, objects other than them may be cooled.

An inert gas, e.g., helium or argon, is enclosed in the inside of thethus configured loop tube 2. This not limited to the above-describedinert gas. A working fluid, e.g., nitrogen or air, may be enclosed.These working fluid is set at 0.1 MPa to 1.0 MPa.

When such a working fluid is enclosed, if helium or the like having asmall Prandtl number and a small specific gravity is used, the timeuntil an acoustic wave is generated can be reduced. However, if such aworking fluid is used, the sound velocity is increased and the heatexchange with the stack inner wall cannot be performed smoothly.Conversely, if argon or the like having a large Prandtl number and alarge specific gravity is used, the viscosity is increased and anacoustic wave cannot be generated rapidly. Consequently, it ispreferable that a mixed gas of helium and argon is used. Theabove-described mixed gas is enclosed as described below.

First, helium having a small Prandtl number and a small specific gravityis enclosed in the loop tube 2, and an acoustic wave is generatedrapidly. Subsequently, a gas, e.g., argon, having a large Prandtl numberand a large specific gravity is injected in order to reduce the soundvelocity of the acoustic wave generated. When this argon is blended, asshown in FIG. 8, a gas injection apparatus 9 is disposed at the centerportion of the connection tube portion 2 b disposed on the upper side,and argon is injected therefrom. Argon is injected uniformly into theright and left linear tube portions 2 a and, thereby, argon having arelatively large specific gravity is allowed to flow downward, so thatthe gas in the inside is made homogeneous. The procedure is not limitedto the above-described case where helium is enclosed in advance and,thereafter, argon is injected. Conversely, argon may be enclosed inadvance and, thereafter, helium may be injected. In this case, when thegas injection apparatus 9 is disposed at the center portion of theconnection tube portion 2 b disposed on the lower side, and helium isinjected therefrom, helium having a relatively small specific gravity isallowed to move upward, so that the gas is made homogeneous. Thepressures of these mixed gases are set at 0.01 MPa to 5 MPa, and in thecase where the entire apparatus is miniaturized, the pressure is set ata relatively low level, for example, 0.01 MPa. In this manner, aninfluence of the viscosity in the miniaturized loop tube 2 can bereduced.

The operation state of the thus configured thermoacoustic apparatus 1will be described below.

First, helium is enclosed in the loop tube 2. Under this condition,water is circulated around the first low-temperature-side heat exchanger5 of the first stack 3 a and the second high-temperature-side heatexchanger 6 of the second stack 3 b. When heat is applied to the firsthigh-temperature-side heat exchanger 4 of the first stack 3 a under thiscondition, a temperature gradient is generated in the first stack 3 adue to the temperature difference between the firsthigh-temperature-side heat exchanger 4 and the firstlow-temperature-side heat exchanger 5, and the working fluid beginswandering minutely. Subsequently, this working fluid begins vibratinglargely and circulates in the loop tube 2. At this time, since thelinear tube portion 2 a including the first stack 3 a is set to berelatively long, the surface wavefront of the acoustic wave generated inthe first stack 3 a is stabilized, and a standing wave and a travelingwave can be generated in a short time in the loop tube 2. The acousticenergy due to the standing wave and the traveling wave is generated inthe direction opposite to the transfer direction (direction from thefirst high-temperature-side heat exchanger 4 toward the firstlow-temperature-side heat exchanger 5) of the thermal energy in thefirst stack 3 a, that is, in the direction from the firstlow-temperature-side heat exchanger 5 toward the firsthigh-temperature-side heat exchanger 4, on the basis of the energyconservation law. The resulting acoustic energy is reflected efficientlyat the corner portions 20 b of the loop tube 2 and the like and,thereafter, is transferred to the second stack 3 b side. The workingfluid is allowed to expand or shrink due to pressure variation andvolume variation of the working fluid based on the standing wave and thetraveling wave on the second stack 3 b side. The thermal energygenerated at that time is transferred in the direction opposite to thetransfer direction of the acoustic energy, that is, from the secondlow-temperature-side heat exchanger 7 toward the secondhigh-temperature-side heat exchanger 6 side. In this manner, the secondlow-temperature-side heat exchanger 7 is cooled and the intended objectis cooled.

In the above-described thermoacoustic apparatus 1, the acoustic wave isgenerated through self excitation by the temperature gradient providedin the first stack 3 a. However, in reality, it takes relatively longtime until the above-described acoustic wave is generated through selfexcitation. On the other hand, it is possible to decrease thefrequencies of the standing wave and the traveling wave by changing thediameter of the loop tube 2 in order to reduce the generation time ofthe standing wave and the traveling wave. However, this results in aninsufficient output. In this case, as shown in FIG. 8, an acoustic wavegenerator 8 may be disposed.

This acoustic wave generator 8 is composed of a speaker, a piezoelectricelement, or other devices which forcedly vibrate the working fluid fromthe outside, and is disposed along the outer perimeter surface of theloop tube 2 or in the inside of the loop tube 2. It is preferable thatthe acoustic wave generator 8 is attached with a distance of one-half orone-quarter the wavelength of the standing wave and the traveling wavegenerated, and preferably, the acoustic wave generator 8 is disposed insuch a way as to forcedly vibrate the working fluid in the axisdirection of the loop tube 2 in correspondence with the movementdirection of the standing wave and the traveling wave. As describedabove, when the acoustic wave generator 8 is disposed, the generationtime of the standing wave and the traveling wave can be reduced, and thesecond low-temperature-side heat exchanger 7 can be cooled.

In the case where satisfactory cooling effect cannot be attained by theabove-described thermoacoustic apparatus 1 alone, a thermoacousticsystem 100, in which a plurality of thermoacoustic apparatuses 1 areconnected, as shown in FIG. 9, may be used. In FIG. 9, referencenumerals 1 a, 1 b . . . and 1 n denote thermoacoustic apparatuses 1configured as described above, and these first thermoacoustic apparatus1 a, second thermoacoustic apparatus 1 b . . . and nth thermoacousticapparatus 1 n are disposed adjacently in series. All firsthigh-temperature-side heat exchangers 4 in these first thermoacousticapparatus 1 a . . . are heated by heaters or the like. On the otherhand, respective second low-temperature-side heat exchangers 7 ofthermoacoustic apparatus 1 a . . . are connected to firstlow-temperature-side heat exchangers 5 of thermoacoustic apparatus 1 badjacent thereto. In this manner, the temperature gradient in the secondthermoacoustic apparatus 1 b can be made larger than the temperaturegradient of the first stack 3 a in the first thermoacoustic apparatus 1a. Consequently, the temperature gradient of the thermoacousticapparatus in can be increased one after another toward the downstream,and the last thermoacoustic apparatus in can output heat at a lowertemperature. When the thermoacoustic apparatuses 1 a . . . are connectedas described above, if each of the thermoacoustic apparatuses 1 a . . .is allowed to generate an acoustic wave through self excitation, ittakes significantly much time until a standing wave and a traveling waveare generated in the last thermoacoustic apparatus 1 n. Consequently, itis preferable that the time until a standing wave and a traveling waveare generated in each of the thermoacoustic apparatuses 1 a . . . isreduced by disposing acoustic wave generators 8, in particular, on theouter perimeter surface or in the inside of the loop tube 2.

In the above-described embodiment, the explanation is performed withreference to the thermoacoustic apparatus 1 in which the first stack 3 aside is heated and the second stack 3 b side is cooled. Conversely, thefirst stack 3 a side may be cooled and the second stack 3 b side may beheated. FIG. 8 shows an example of this thermoacoustic apparatus 1.

In FIG. 10, the elements indicated by the same reference numerals asthose in FIG. 1 to FIG. 8 are elements having the same structures as theelements set forth above. In FIG. 10, a first stack 3 a is disposedabove the center of a linear tube portion 2 a, and a second stack 3 b isdisposed at an appropriate position in the linear tube portion 2 aopposite thereto. With respect to the positions of installation of thefirst stack 3 a and the second stack 3 b, it is preferable that theseare disposed at the positions at which the installation condition is thesame as the condition in the above-described embodiment. Low-temperatureheat at minus several tens of degrees or lower is input into the firstlow-temperature-side heat exchanger 5 and, in addition, an antifreezeliquid is circulated in a first high-temperature-side heat exchanger 4and a second low-temperature-side heat exchanger 7. Consequently, anacoustic wave is generated through self excitation by the temperaturegradient formed in the first stack 3 a on the basis of the principle ofthermoacoustic effect, the surface wavefront is stabilized in the lineartube portion 2 a set to be relatively long, and a standing wave and atraveling wave are generated rapidly through the use of a downdraft ofthe low-temperature heat. The acoustic energy of the standing wave andthe traveling wave is generated in such a way that the movementdirection thereof is a direction opposite to the transfer direction(direction from the first high-temperature-side heat exchanger 4 towardthe first low-temperature-side heat exchanger 5) of the thermal energyin the first stack 3 a. The acoustic energy due to the standing wave andthe traveling wave is reflected efficiently at the corner portions 20 bof the loop tube 2 and the like and, thereafter, is transferred to thesecond stack 3 b side. The working fluid is allowed to repeat expansionand shrinkage due to pressure variation and volume variation of theworking fluid based on the standing wave and the traveling wave on thesecond stack 3 b side. The thermal energy generated at that time istransferred in the direction opposite to the transfer direction of theacoustic energy, that is, from the second low-temperature-side heatexchanger 7 toward the second high-temperature-side heat exchanger 6side. In this manner, the second high-temperature-side heat exchanger 6is heated.

In the present embodiment as well, in order to facilitate the generationof the standing wave and the traveling wave, an acoustic wave generator8 may be disposed on the outer perimeter surface or in the inside of theloop tube 2. Alternatively, the above-described thermoacousticapparatuses 1 may be connected as shown in FIG. 9, andhigher-temperature heat may be output from the thermoacoustic apparatus1 on the end side.

According to the above-described embodiments, a pair of linear tubeportions 2 a having the same length are disposed along the verticaldirection, connection tube portions 2 b for connecting the linear tubeportions 2 a are disposed, and the linear tube portions 2 b are set tobe longer than the connection tube portions 2 b. Under this condition,the first stack 3 a sandwiched between the first high-temperature-sideheat exchanger 4 and the first low-temperature-side heat exchanger 5 isdisposed in the linear tube portion 2 a. Consequently, the surfacewavefront of the acoustic wave generated through self excitation in thefirst stack 3 a can be stabilized in the long linear tube portion 2 a.Since the first stack 3 a is disposed in the linear tube portion 2 aalong the vertical direction, the time until the acoustic wave isgenerated can be reduced through the use of an updraft or a downdraftgenerated on the first stack 3 a side. Furthermore, after the acousticwave is generated, the efficiency of heat exchange can be improved.

In the configuration of the above-described loop tube 2, when the lengthof the linear tube portion and the length of the connection tube portionare assumed to be La and Lb, respectively, La and Lb are set within therange satisfying “1:0.01≦La:Lb<1:1”, more preferably, La and Lb are setwithin the range satisfying “La:Lb≦1:0.5”. Therefore, the surfacewavefront of the generated acoustic wave can be stabilized more rapidly.

In the above-described apparatus, in the case where the first stack 3 aside is heated and the second stack 3 b side is cooled, the first stack3 a is disposed below the center of the linear tube portion 2 a.Therefore, a space for generation of an updraft due to the heat appliedto the first high-temperature-side heat exchanger 4 can be ensured, andthe standing wave and the traveling wave can be generated rapidlythrough the use of the updraft.

Conversely, in the case where the first stack 3 a side is cooled and thesecond stack 3 b side is heated, the first stack 3 a is disposed abovethe center of the linear tube portion 2 a. Therefore, a space forgeneration of a downdraft due to the low-temperature heat applied to thefirst low-temperature-side heat exchanger 5 can be ensured, and thestanding wave and the traveling wave can be generated rapidly throughthe use of the downdraft.

In addition, when one end of the linear tube portion 2 a is connected toone end of the connection tube portion 2 b, an intersection of therespective center axes is assumed to be a start point of a circuit, andan entire length of the circuit is assumed to be 1.00, the center of thefirst stack 3 a is set at a position corresponding to 0.28±0.05 relativeto the entire length of the circuit. Consequently, the acoustic wavethrough self excitation can be generated more rapidly.

When an entire length of the circuit is assumed to be 1.00, a first peakof the pressure variation of a working fluid along the circuit ispresent in the vicinity of the first stack, and a second peak is presentat a position corresponding to about one-half the entire length of thecircuit, the second stack 3 b is disposed in such a way that the centerof the second stack 3 b is positioned past the above-described secondpeak. Consequently, the cooling efficiency or the heating efficiency inthe second stack 3 b can be increased.

Since the acoustic wave generator 8 for generating the standing wave andthe traveling wave is disposed on the outer perimeter portion or in theinside of the loop tube 2, the standing wave and the traveling wave canbe generated more rapidly not only by the acoustic wave through selfexcitation, but also by forced vibration from the acoustic wavegenerator 8.

As shown in FIG. 4, the stack 3 c including connection channels 30arranged in such a way that the inner diameters of individual connectionchannels are increased one after another as the position of theconnection channel approaches the outside can also be used in place ofthe first stack 3 a and the second stack 3 b. Consequently, the innerdiameters of the connection channels 30 in the vicinity of the boundarylayer in the inside of the loop tube 2 can be increased, and the energyexchange in this portion can be performed efficiently.

As shown in FIG. 5, the stack 3 d including connection channels 30arranged in such a way that the inner diameters of individual connectionchannels are decreased one after another as the position of theconnection channel approaches the outside, can also be used in place ofthe first stack 3 a and the second stack 3 b. Consequently, the innerdiameters of the connection channels 30 in the center portion in theinside of the loop tube 2 can be increased, and the energy exchange inthis portion can be performed efficiently.

Alternatively, as shown in FIG. 6, the stack 3 e including meanderingconnection channels 30 can also be used in place of the first stack 3 aand the second stack 3 b. Consequently, large surface areas of theworking fluid and the stack 3 e can be ensured, the heat exchange withthe working fluid is facilitated and, thereby, higher-temperature heatcan be output.

Alternatively, as shown in FIG. 7, the stack 3 f including connectionchannels arranged in such a way that the flow path lengths of individualconnection channels are decreased one after another as the position ofthe connection channel approaches the outside may be used in place ofthe first stack 3 a and the second stack 3 b. Consequently, the flowpath lengths of connection channels close to the boundary layer of theloop tube 2 can be decreased, the speed gradient is made uniform as awhole and, thereby, the heat exchangers 4, 5, 6, and 7 can be uniformlyheated or cooled altogether.

The material used for the first stack 3 a and the second stack 3 b iscomposed of at least one type of ceramic, sintered metal, gauze, andnonwoven metal fabric, and the ωτ (ω: an angular frequency of theworking fluid, τ: temperature relaxation time) thereof is set to becomewithin the range of 0.2 to 20. Consequently, an acoustic wave can begenerated through self excitation more rapidly and efficiently.

Furthermore, as shown in FIG. 9, a plurality of the above-describedthermoacoustic apparatuses 1 are disposed, wherein a secondlow-temperature-side heat exchanger 7 in one thermoacoustic apparatus 1is connected to a first low-temperature-side heat exchanger 5 in anotherthermoacoustic apparatus 1 adjacent thereto, or a secondhigh-temperature-side heat exchanger 6 in one thermoacoustic apparatus 1is connected to a first high-temperature-side heat exchanger 4 inanother thermoacoustic apparatus 1 adjacent thereto. Consequently, thetemperature gradient in the first stack 3 a can be increased one afteranother on an adjacent thermoacoustic apparatus 1 basis,higher-temperature heat or lower-temperature heat can be output from thethermoacoustic apparatus 1 on the end side.

The present invention is not limited to the above-described embodiments,and can be carried out in various forms.

For example, in the above-described embodiments, bilaterally symmetricloop tube 2 is disposed. However, not limited to this, and anirregularly meandering loop tube may be used. In this case, it ispreferable that a first stack 3 a serving as an acoustic wave generationsource is disposed in the longest linear tube portion.

In the above-described embodiments, linear tube portions 2 a along thevertical direction are disposed. However, not limited to this, and alinear tube portion slightly inclined relative to the ground may bedisposed.

The positions of the above-described first stack 3 a and the secondstack 3 b are not limited to the conditions set as described above, andthey may be disposed at appropriately positions on the basis of variousexperiments or the like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a thermoacoustic apparatus according toan embodiment of the present invention.

FIG. 2 is a diagram showing a magnified corner portion of a loop tube inthe above-described embodiment.

FIG. 3 is a diagram showing the shape of a corner portion of a loop tubein another embodiment.

FIG. 4 is a diagram showing the shape of a stack in another embodiment.

FIG. 5 is a diagram showing the shape of a stack in another embodiment.

FIG. 6 is a diagram showing the shape of a stack in another embodiment.

FIG. 7 is a diagram showing the shape of a stack in another embodiment.

FIG. 8 is a schematic diagram of a thermoacoustic apparatus including anacoustic wave generator.

FIG. 9 is a schematic diagram of an acoustic heating system in whichacoustic heating apparatuses are connected.

FIG. 10 is a schematic diagram of a thermoacoustic apparatus in anotherembodiment.

REFERENCE NUMERALS

-   1 . . . thermoacoustic apparatus-   2 . . . loop tube-   2 a . . . linear tube portion-   2 b . . . connection tube portion-   20 b . . . corner portion-   3 a . . . first stack-   3 b . . . second stack-   3 c . . . stack-   3 d . . . stack-   3 e . . . stack-   3 f . . . stack-   30 . . . connection channel-   4 . . . first high-temperature-side heat exchanger-   5 . . . first low-temperature-side heat exchanger-   6 . . . second high-temperature-side heat exchanger-   7 . . . second low-temperature-side heat exchanger-   8 . . . acoustic wave generator-   9 . . . gas injection apparatus-   100 . . . thermoacoustic system

1. A thermoacoustic apparatus comprising a first stack sandwichedbetween a first high-temperature-side heat exchanger and a firstlow-temperature-side heat exchanger and a second stack sandwichedbetween a second high-temperature-side heat exchanger and a secondlow-temperature-side heat exchanger in the inside of a loop tube,wherein a standing wave and a traveling wave are generated through selfexcitation by heating the first high-temperature-side heat exchanger,the second low-temperature-side heat exchanger is cooled by the standingwave and the traveling wave, or/and a standing wave and a traveling waveare generated through self excitation by cooling the firstlow-temperature-side heat exchanger, and the secondhigh-temperature-side heat exchanger is heated by the standing wave andthe traveling wave, the thermoacoustic apparatus characterized in thatthe loop tube is configured to include a plurality of linear tubeportions, which stand relative to the ground, and connection tubeportions shorter than the linear tube portions, and the first stack isdisposed in the longest linear tube portion among the plurality oflinear tube portions.
 2. The thermoacoustic apparatus according to claim1, wherein when the lengths of the linear tube portion and theconnection tube portion are assumed to be La and Lb, respectively, Laand Lb are set within the range satisfying1:0.01≦La:Lb<1:1.
 3. The thermoacoustic apparatus according to claim 1,in which a standing wave and a traveling wave are generated through selfexcitation by heating the first high-temperature-side heat exchanger,and the second low-temperature-side heat exchanger is cooled by thestanding wave and the traveling wave, wherein the first stack isdisposed below the center of the linear tube portion.
 4. Thethermoacoustic apparatus according to claim 1, in which a standing waveand a traveling wave are generated through self excitation by coolingthe first low-temperature-side heat exchanger, and the secondhigh-temperature-side heat exchanger is heated by the standing wave andthe traveling wave, wherein the first stack is disposed above the centerof the linear tube portion.
 5. The thermoacoustic apparatus according toclaim 1, wherein when one end of the linear tube portion is connected toone end of the connection tube portion, an intersection of therespective center axes is assumed to be a start point of a circuit, andan entire length of the circuit is assumed to be 1.00, the center of thefirst stack is set at a position corresponding to 0.28±0.05 relative tothe entire length of the circuit.
 6. The thermoacoustic apparatusaccording to claim 1, wherein when an entire length of the circuit isassumed to be 1.00, a first peak of the pressure variation of a workingfluid along the circuit is present in the vicinity of the first stack,and a second peak is present at a position corresponding to aboutone-half the entire length of the circuit, the second stack is disposedin such a way that the center of the second stack is positioned past thesecond peak.
 7. The thermoacoustic apparatus according to claim 1,wherein an acoustic wave generator for generating the standing wave andthe traveling wave is disposed on the outer perimeter portion or in theinside of the loop tube.
 8. The thermoacoustic apparatus according toclaim 1, wherein the first stack or/and the second stack includeconnection channels arranged in such a way that the inner diameters ofindividual connection channels are increased one after another as theposition of the connection channel approaches the outside.
 9. Thethermoacoustic apparatus according to claim 1, wherein the first stackor/and the second stack include connection channels arranged in such away that the inner diameters of individual connection channels aredecreased one after another as the position of the connection channelapproaches the outside.
 10. The thermoacoustic apparatus according toclaim 1, wherein the first stack or/and the second stack includemeandering connection channels.
 11. The thermoacoustic apparatusaccording to claim 1, wherein the first stack or/and the second stackinclude connection channels arranged in such a way that the flow pathlengths of individual connection channels are decreased one afteranother as the position of the connection channel approaches theoutside.
 12. The thermoacoustic apparatus according to claim 1, whereina material for the first stack or/and the second stack is composed of atleast one type of ceramic, sintered metal, gauze, and nonwoven metalfabric, and the ωτ (ω: an angular frequency of the working fluid, τ:temperature relaxation time) thereof is configured to become within therange of 0.2 to
 20. 13. A thermoacoustic system comprising a pluralityof thermoacoustic apparatuses according to claim 1, wherein a secondlow-temperature-side heat exchanger in one thermoacoustic apparatus isconnected to a first low-temperature-side heat exchanger in anotherthermoacoustic apparatus adjacent thereto, or a secondhigh-temperature-side heat exchanger in one thermoacoustic apparatus isconnected to a first high-temperature-side heat exchanger in anotherthermoacoustic apparatus adjacent thereto.